Porous paper machine clothing comprises long, wide belts which circulate in different parts of a paper machine and on which the paper web is conveyed through the paper machine. In the first part, which is termed the sheet forming section, a fibrous pulp is deposited on the paper machine clothing, whereupon a web of fibrous material is formed. This is dewatered through the paper machine clothing. The paper machine clothing consists of a textile filament product which is sufficiently porous for the liquid which originates from the web of fibrous material to be conveyed away through the paper machine clothing as a result of the effect of gravity and reduced pressure. In the subsequent press section, the paper web and the paper machine clothing are passed through roll presses so that the liquid which still remains in the paper web is pressed out through the paper machine clothing. In general, the paper machine clothing is formed as a felt comprising a support made of a textile filament product. In the subsequent drying section, the paper web and the paper machine clothing are passed over heated rolls, whereby further de-watering occurs—which is more precisely termed drying in this case. In the drying section, paper machine clothing which consists of filament-containing products is mainly used, i.e. as a drying screen, which is also porous, in order to convey the vapour away via the pores.
These textile filament products are mainly formed as woven fabrics. In addition, what are termed filament lay-ups are also known, in which the filaments are not bound to each other, i.e. they are not woven to or meshed with each other. U.S. Pat. No. 3,097,413 discloses paper machine clothing such as this. It has a filament lay-up comprising a layer of longitudinal filaments which extend parallel to and at a distance from each other, and which are not joined to each other. A fibrous felt, which surrounds the longitudinal filaments and which is needle-bonded thereto, is applied to this layer.
Paper machine clothing such as this only has a low transverse strength, however. A change has therefore been made to the use of a combination of a layer of longitudinal filaments with a layer of transverse filaments (DE-A-1 802 560; EP-B-0 394 293). In this procedure, modules consisting of a fibrous layer and of a fibrous web needle-bonded thereto are first formed, and these modules are combined and are needle-bonded again. This manner of production is not suitable for paper machine clothing which consists of one filament-containing product only. In this situation, U.S. Pat. No. 4,555,440 proposes that the individual filament layers be joined to each other by binding filaments.
In particular, in the aforementioned paper machine clothing of this type, the resistance to displacement between the individual layers, and thus the dimensional stability, is unsatisfactory. If binding filaments are used, they constitute extraneous bodies and significantly complicate the manufacturing process. In order to eliminate these disadvantages, U.S. Pat. No. 5,888,915 proposes that the layers of longitudinal and transverse filaments are laid directly on each other and are fused to each other by heating at their crossing points. The pre-requisite for this, however, is that two-component filaments are used in which the filament core has a higher melting temperature than the filament cladding. Fusion occurs by heating to a temperature above the melting point of the filament cladding and below the melting point of the filament core.
Due to the direct bonding of the filaments of the individual layers, the dimensional stability of the paper machine clothing is improved. One disadvantage, however, is that special filaments, namely two-component filaments, have to be used. These are expensive, and their material properties cannot always be adjusted in the optimum manner to suit the conditions in the respective part of the paper machine.